Light emitting device and method of manufacturing the same

ABSTRACT

Provided are a light emitting device and a method of manufacturing the same. A light emitting device includes an active layer; a first conductive semiconductor layer on the active layer; a second conductive semiconductor layer on the active layer so that the active layer is disposed between the first and second conductive semiconductor layers; and a photonic crystal structure comprising a first light extraction pattern on the first conductive semiconductor layer having a first period, and second light extraction pattern on the first conductive semiconductor layer having a second period, the first period being greater than λ/n, and the second period being identical to or smaller than λ/n, where n is a refractive index of the first conductive semiconductor layer, and λ is a wavelength of light emitted from the active layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 to KoreanPatent Application No. 10-2008-0117851 filed on Nov. 26, 2008, which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a light emitting deviceand a method of manufacturing the same.

The wavelength of light emitted from a light emitting diode depends onthe semiconductor material used to manufacture the light emitting diode.This is because the wavelength of emitted light depends on the band-gapof a semiconductor material that represents an energy difference betweenvalence band electrons and conduction band electrons.

With recent increases in luminance of light emitting diodes, the lightemitting diodes are being used as light sources for displays, vehicles,and illumination devices. Also, light emitting diodes that emit a highlyefficient white colored light can be implemented by using a fluorescentsubstance or by combining various colors of light emitting diodes.

On the other hand, the luminance of a light emitting diode depends onvarious conditions such as the structure of an active layer, a lightextraction structure that extracts light to the outside, chip size, andthe type of molding member surrounding a light emitting diode.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a light emitting devicehaving new light extraction structure, and a method of manufacturing thesame.

Embodiments of the present invention also provide a light emittingdevice having improved light extraction efficiency, and a method ofmanufacturing the same.

In one embodiment a light emitting device includes an active layer; afirst conductive semiconductor layer on the active layer; a secondconductive semiconductor layer on the active layer so that the activelayer is disposed between the first and second conductive semiconductorlayers; and a photonic crystal structure comprising a first lightextraction pattern on the first conductive semiconductor layer having afirst period, and second light extraction pattern on the firstconductive semiconductor layer having a second period, the first periodbeing greater than λ/n, and the second period being identical to orsmaller than λ/n, where n is a refractive index of the first conductivesemiconductor layer, and λ is a wavelength of light emitted from theactive layer.

In another embodiment, a light emitting device includes an active layer;a first conductive semiconductor layer on the active layer; a secondconductive semiconductor layer on the active layer so that the activelayer is disposed between the first and second conductive semiconductorlayers; a non-conductive semiconductor layer on the first conductivesemiconductor layer; and a photonic crystal structure comprising a firstlight extraction pattern on the non-conductive semiconductor layerhaving a first period, and a second light extraction pattern on thenon-conductive semiconductor layer having a second period, the firstperiod being greater than λ/n, and the second period being identical toor smaller than λ/n, where n is a refractive index of the non-conductivesemiconductor layer, and λ is a wavelength of light emitted from theactive layer.

In another embodiment, a light emitting device includes a light emittingsemiconductor layer; a first electrode layer on the light emittingsemiconductor layer; a second electrode layer on the light emittingsemiconductor layer so that the light emitting semiconductor layer isdisposed between the first and second electrode layers; and a photoniccrystal structure comprising a first light extraction pattern having afirst period on an average in a traveling direction of light emittedfrom the light emitting semiconductor layer, and a second lightextraction pattern having a second period on an average, the firstperiod being greater than λ/n, and the second period being identical toor smaller than λ/n, where n is a refractive index of a materialcomprising the photonic crystal structure, and λ is a wavelength of thelight emitted from the light emitting semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a light emitting device according to afirst embodiment of the present invention.

FIGS. 2 to 5 are views illustrating a light emitting device and a methodof manufacturing the same according to a second embodiment of thepresent invention.

FIG. 6 is a view illustrating the light emitting device of FIG. 1.

FIG. 7 is graph illustrating an incident angle and a transmittance oflight incident to a photonic crystal in a light emitting deviceaccording to an embodiment of the present invention.

FIG. 8 is a graph illustrating a variation of an optical power withrespect to a current strength in a light emitting device according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the description of embodiments, it will be understood that when alayer (or film), region, pattern or structure is referred to as being‘on’ or ‘under’ another layer (or film), region, pad or pattern, theterminology of ‘on’ and ‘under’ includes both the meanings of ‘directly’and ‘indirectly’. Further, the reference about ‘on’ and ‘under’ eachlayer will be made on the basis of drawings.

In the drawings, the thickness or size of each layer is exaggerated,omitted, or schematically illustrated for convenience in description andclarity. Also, the size of each element does not necessarily reflect anactual size thereof.

Hereinafter, a light emitting device and a method of manufacturing thelight emitting device will be described in detail with reference to theaccompanying drawings.

FIG. 1 is a view illustrating a light emitting device according to afirst embodiment of the present invention.

Referring to FIG. 1, the light emitting device includes a secondelectrode layer 50, a light emitting semiconductor layer 20, and a firstelectrode layer 60. The light emitting semiconductor layer 20 is formedon the second electrode layer 50. The first electrode layer 60 is formedon the light emitting semiconductor layer 20.

The second electrode layer 50 may include an ohmic contact layer 51, areflection layer 52, and a conductive substrate 53. For example, theconductive substrate 53 may be formed of at least one of Cu, Ti, Cr, Ni,Al, Pt, Au, W, and a conductive semiconductor material. The reflectionlayer 52 may be formed of at least one of Ag, Al, Cu, and Ni, which hashigh reflectance. The ohmic contact layer 51 may be formed of atransparent electrode layer, for example, at least one of ITO, ZnO,RuO_(x), TiO_(x), and IrO_(x).

The light emitting semiconductor layer 20 includes a first conductivesemiconductor layer 23, an active layer 22, and a second conductivesemiconductor layer 21. The light emitting semiconductor layer 20 may beformed of a GaN-based semiconductor layer. Here, when the firstconductive semiconductor layer 23 is an N-type semiconductor layer, thesecond conductive semiconductor layer 21 may be a P-type semiconductorlayer. When the first conductive semiconductor layer 23 is a P-typesemiconductor layer, the second conductive semiconductor layer 21 may bean N-type semiconductor layer.

A first electrode layer 60 is formed on the first conductivesemiconductor layer 23. The first electrode layer 60 provides power tothe active layer 22 in conjunction with the second electrode layer 50.

On the other hand, a photonic crystal (or a photonic crystal structure)is formed on the first conductive semiconductor layer 23 to increase alight extraction efficiency.

The photonic crystal includes a first light extraction pattern 40including a plurality of holes 41 formed in the first conductivesemiconductor layer 23 at (or having) a first period, and a second lightextraction pattern 70 including a plurality of minute protrusions 71 onthe first conductive semiconductor layer 23 at (or having) a secondperiod.

Although it is described as an example in FIG. 1 that the holes 41 andthe minute protrusion 71 are periodically formed in the first lightextraction pattern 40 and the second light extraction pattern 70 byetching the first conductive semiconductor layer 23, respectively, suchis not required, and protrusions may be formed as the first lightextraction pattern 40, or minute holes may be formed as the second lightextraction pattern 70.

In the embodiment, the holes 41 have a depth of about 225 nm, but suchis not required, and the holes 41 have may have a depth that is variedaccording to design, or other depths.

The plurality of minute protrusion 71 may be formed by wet-etching ordry-etching the first conductive semiconductor layer 23 where the firstlight extraction pattern 40 is formed, or may be formed through acoating, a vapor deposition, a growth process, or another process.

The plurality of minute protrusions 71 in the second light extractionpattern 70 of FIG. 1 are formed using Ag. For example, the plurality ofminute protrusions 71 may be formed by etching the first conductivesemiconductor layer 23 using Ag as a mask. Here, when Ag is deposited ina thin thickness of about 10 nm, Ag (such as Ag atoms or particles)becomes partially stuck to each other. This is referred to as aclustering effect.

FIG. 6 is a plan view illustrating the light emitting device of FIG. 1.

As illustrated in FIG. 6, the first light extraction pattern 40 includesthe plurality of holes 41 that are disposed at (or having) a firstperiod on the average, and the second light extraction pattern 70includes the plurality of minute protrusions 71 that are disposed at (orhaving) a second period on the average. The first period (or the firstperiod on the average) refers to a mean value of distances between thecenters of the plurality of holes 41 that are adjacent. The secondperiod (or the second period on the average) refers to a mean value ofdistances between the centers of the plurality of minute protrusions 71that are adjacent. In other embodiments, the first period and/or thesecond period may be predetermined. Similarly, reference to an average

The first light extraction pattern 40 may be regularly disposed (orformed regularly), and the second light extraction pattern 70 may beirregularly disposed (or formed irregularly).

In the embodiment, the first period is designed to be greater than λ/n,and the second period is designed to be identical to or smaller thanλ/n. Here, n is the refractive index of the first conductivesemiconductor layer 23, and λ is the wavelength of light emitted fromthe active layer 22. Light extraction efficiency of light emitted fromthe active layer 22 that is extracted to the outside through the firstconductive semiconductor layer 23 may depend on the photonic crystal.For example, when a light extraction pattern period of the photoniccrystal is greater than λ/n, light having an incident angle greater thana critical angle may be more efficiently extracted. When a lightextraction pattern period of the photonic crystal is identical to orsmaller than λ/n, light having an incident angle less than the criticalangle may be more efficiently extracted.

The light emitting device according to the embodiment may maximize thelight extraction efficiency by including a first light extractionpattern 40 formed at (or having) the first period, and a second lightextraction pattern 70 formed at (or having) the second period.

In particular, the second light extraction pattern 70 where the lightextraction pattern period of the photonic crystal is identical to orsmaller than λ/n has an anti-reflective coating effect on an incidentlight having a critical angle or less to allow light emitted from theactive layer 22 to be effectively extracted.

In example embodiments of the present invention, when the firstconductive semiconductor layer 23 is GaN, the refractive index n may beabout 2.2 to about 2.3. In example embodiments of the present invention,the wavelength of light λ emitted from the active layer 22 may be about450 nm to about 490 nm. In other embodiments, other wavelengths of lightλ may be emitted from the active layer 22 depending on a refractiveindex of a material that is used for the first conductive semiconductorlayer 23.

FIG. 7 is a graph illustrating an incident angle and a transmittance oflight entered into a photonic crystal in a light emitting deviceaccording to an embodiment of the present invention. FIG. 8 is a graphillustrating a variation of an optical power with respect to the currentstrength in a light emitting device according to an embodiment of thepresent invention.

FIGS. 7 and 8 show three cases, including a case having no photoniccrystal, a case having a first light extraction pattern, and a casehaving first and second extraction patterns.

In a light emitting device including no photonic crystal, when anincident angle of light emitted to the outside through the top surfaceof the first conductive semiconductor layer ranges from zero to acritical angle, its maximum transmittance is about 0.9 at the incidentangle of 0°. Here, transmittance is significantly reduced as theincident angle approaches the critical angle. The critical angle isabout 35°. When the incident angle is greater than the critical angle,light is not transmitted.

In a light emitting device including a first light extraction pattern asa photonic crystal, when an incident angle of light emitted to theoutside through the first light extraction pattern ranges from 0° to acritical angle, its transmittance is smaller than that of the lightemitting device having no photonic crystal. However, light istransmitted even when the incident angle is greater than the criticalangle.

In a light emitting device including first and second light extractionpatterns as a photonic crystal, when an incident angle of light emittedto the outside through the first and second light extraction patternsranges 0° to a critical angle, its transmittance is higher than those ofthe light emitting device having no photonic crystal or the lightemitting device having only the first light extraction pattern. Light istransmitted similar to the light emitting device having the firstextraction pattern even when the incident angle is greater than thecritical angle.

Also, as the current strength increases, the optical power of the lightemitting device having the first and second light extraction patterns isgreater than those of others.

FIGS. 2 to 5 are views illustrating a light emitting device and a methodof manufacturing the same according to a second embodiment of thepresent invention. To explain the second embodiment, detaileddescription of parts identical to those of the first embodiment will beomitted.

Referring to FIG. 5, the light emitting device according to the secondembodiment includes a second electrode layer 50, a light emittingsemiconductor layer 20, a first electrode layer 60, and a non-conductivesemiconductor layer 24. The light emitting semiconductor layer 20 isformed on the second electrode layer 50. The first electrode layer 60 isformed on the light emitting semiconductor layer 20. The non-conductivesemiconductor layer 24 is also formed on the light emittingsemiconductor layer 20.

The second electrode layer 50 includes an ohmic contact layer 51, areflection layer 52, and a conductive substrate 53. For example, theconductive substrate 53 may be formed of at least one of Cu, Ti, Cr, Ni,Al, Pt, Au, W, and a conductive semiconductor material. The reflectionlayer 52 may be formed of at least one of Ag, Al, Cu, and Ni, which hashigh reflectance. The ohmic contact layer 51 may be formed of atransparent electrode layer, for example, at least one of ITO, ZnO,RuO_(x), TiO_(x), and IrO_(x).

The light emitting semiconductor layer 20 includes a first conductivesemiconductor layer 23, an active layer 22, and a second conductivesemiconductor layer 21. The light emitting semiconductor layer 20 may beformed of a GaN-based semiconductor layer. Here, when the firstconductive semiconductor layer 23 is an N-type semiconductor layer, thesecond conductive semiconductor layer 21 may be a P-type semiconductorlayer. When the first conductive semiconductor layer 23 is a P-typesemiconductor layer, the second conductive semiconductor layer 21 may bean N-type semiconductor layer.

A first electrode layer 60 may be formed on the first conductivesemiconductor layer 23. The first electrode layer 60 provides power tothe active layer 22 in conjunction with the second electrode layer 50.

The non-conductive semiconductor layer 24 refers to a semiconductorlayer formed of a material having much smaller electrical conductivitythan those of the first and second conductive semiconductor layers 23and 21. For example, the non-conductive semiconductor layer 24 may beformed of an un-doped GaN layer.

On the other hand, a photonic crystal (or a photonic crystal structure)is formed on the non-conductive semiconductor layer 24 to increase lightextraction efficiency.

The photonic crystal includes a first light extraction pattern 40including a plurality of holes 41 formed in the non-conductivesemiconductor layer 24, and a second light extraction pattern 70including a plurality of minute protrusions 71 on the non-conductivesemiconductor layer 24. Also, the second light extraction pattern 70 maybe formed on a portion of the first conductive semiconductor layer 23.

Unlike the first embodiment, the first and second light extractionpatterns 40 and 70 are formed on the non-conductive semiconductor layer24 in the light emitting device according to the second embodiment.

When the first light extraction pattern 40 is formed on thenon-conductive semiconductor layer 24, the depth of the holes 41 can beincreased. Although not shown in the drawings, the first lightextraction pattern 40 can be formed by etching the non-conductivesemiconductor layer 24 and the first conductive semiconductor layer 23to increase the depth of the holes 41.

When the first and second light extraction patterns 40 and 70 are formedon the non-conductive semiconductor layer 24, an etched region of thefirst conductive semiconductor layer 23 is reduced. Accordingly, thefirst conductive semiconductor layer 23 can be reduced or prevented frombeing damaged during an etching process.

Hereinafter, the method of manufacturing the light emitting deviceaccording to the second embodiment will be described in detail withreference to FIGS. 2 to 5.

Referring to FIG. 2, a non-conductive semiconductor layer 24 is formedon the growth substrate 10. A light emitting semiconductor layer 20 anda second electrode layer 50 is formed on the non-conductivesemiconductor layer 24.

For example, the growth substrate 10 may be formed of a sapphiresubstrate. A buffer layer may be interposed between the growth substrate10 and the non-conductive semiconductor layer 24.

The non-conductive semiconductor layer 24 may be formed of an un-dopedGaN layer.

Referring to FIG. 3, the growth substrate 10 is removed from thenon-conductive semiconductor layer 24. For example, the growth substrate10 may be removed through a laser absorption method. Other removalmethods may include a laser ablation method or a liftoff method.

Referring to FIG. 4, a first light extraction pattern 40 is formed byselectively removing the non-conductive semiconductor layer 24. Thenon-conductive semiconductor layer and the first conductivesemiconductor layer 23 are selectively removed to expose a portion ofthe first conductive semiconductor layer 23.

Referring to FIG. 5, a second light extraction pattern 70 is realized byforming a plurality of minute protrusions 71 on the first lightextraction pattern 40. A first electrode layer 60 is formed on the firstconductive semiconductor layer 23.

The plurality of minute protrusions 71 may be formed using a phenomenonwhere Ag (Ag atoms or particles) become stuck to each other when Ag isdeposited in a thin thickness of about nm or less. More specifically,the plurality of minute protrusions 71 may be formed by selectivelyetching the non-conductive semiconductor layer 24 and/or the firstconductive semiconductor layer 23 using the Ag stuck to each other as amask.

When the growth substrate 10 and the non-conductive semiconductor layer24 in FIG. 3 are removed, and the first light extraction pattern 40 andthe second light extraction pattern 70 are formed, the light emittingdevice according to the first embodiment described in FIG. 1 can bemanufactured. In embodiments of the present invention, thenon-conductive semiconductor layer 24 may be GaN, which may becompletely free of doping impurities, or may include unintentionallydoped impurities.

In example embodiments of the present invention, when the non-conductivesemiconductor layer 24 and/or the first conductive semiconductor layer23 is GaN, the refractive index n may be about 2.2 to about 2.3. Inexample embodiments of the present invention, the wavelength of light λemitted from the active layer 22 may be about 450 nm to about 490 nm. Inother embodiments, other wavelengths of light λ may be emitted from theactive layer 22 depending on a refractive index of a material that isused for the non-conductive semiconductor layer 24 and/or the firstconductive semiconductor layer 23.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., refers to particular feature,structure, or characteristic described in connection with at least oneembodiment of the present invention. The appearances of such phrases invarious places in the specification are not necessarily all referring tothe same embodiment. Further, when a particular feature, structure, orcharacteristic is described in connection with any embodiment, it iswithin the purview of one skilled in the art to effect such feature,structure, or characteristic in connection with other ones of theembodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A light emitting device, comprising: an active layer; a firstconductive semiconductor layer on the active layer; a second conductivesemiconductor layer under the active layer so that the active layer isdisposed between the first and second conductive semiconductor layers;and a photonic crystal structure comprising a first light extractionpattern on the first conductive semiconductor layer having a firstperiod, and a second light extraction pattern on the first conductivesemiconductor layer having a second period, the first period beinggreater than λ/n, and the second period being identical to or smallerthan λ/n, where n is a refractive index of the first conductivesemiconductor layer, and λ is a wavelength of light emitted from theactive layer.
 2. The light emitting device of claim 1, furthercomprising: a second electrode layer under the second conductivesemiconductor layer; and a first electrode layer on the first conductivesemiconductor layer.
 3. The light emitting device of claim 1, whereinthe first light extraction pattern comprises holes and protrusions. 4.The light emitting device of claim 1, wherein the second lightextraction pattern comprises protrusions.
 5. The light emitting deviceof claim 1, wherein the first light extraction pattern is formed in aregular pattern, and the second light extraction pattern is formed in anirregular pattern.
 6. The light emitting device of claim 2, wherein thesecond electrode layer comprises an ohmic layer on the second conductivesemiconductor layer, a reflection layer on the ohmic layer, and aconductive substrate on the reflection layer.
 7. The light emittingdevice of claim 6, wherein the ohmic layer comprises a transparentelectrode layer.
 8. A light emitting device, comprising: an activelayer; a first conductive semiconductor layer on the active layer; asecond conductive semiconductor layer under the active layer so that theactive layer is disposed between the first and second conductivesemiconductor layers; a non-conductive semiconductor layer on the firstconductive semiconductor layer; and a photonic crystal structurecomprising a first light extraction pattern on the non-conductivesemiconductor layer having a first period, and a second light extractionpattern on the non-conductive semiconductor layer having a secondperiod, the first period being greater than λ/n, and the second periodbeing identical to or smaller than λ/n, where n is a refractive index ofthe non-conductive semiconductor layer, and λ is a wavelength of lightemitted from the active layer.
 9. The light emitting device of claim 8,further comprising: a second electrode layer under the second conductivesemiconductor layer; and a first electrode layer on the first conductivesemiconductor layer.
 10. The light emitting device of claim 8, whereinthe first light extraction pattern comprises holes and protrusions. 11.The light emitting device of claim 8, wherein the second lightextraction pattern comprises protrusions.
 12. The light emitting deviceof claim 8, wherein the first light extraction pattern is formed in aregular pattern, and the second light extraction pattern is formed in anirregular pattern.
 13. The light emitting device of claim 9, wherein thesecond electrode layer comprises an ohmic layer on the second conductivesemiconductor layer, a reflection layer on the ohmic layer, and aconductive substrate on the reflection layer.
 14. The light emittingdevice of claim 13, wherein the ohmic layer comprises a transparentelectrode layer.
 15. The light emitting device of claim 9, wherein thefirst electrode layer is formed on a region of the first conductivesemiconductor layer from which the non-conductive semiconductor layerand a portion of the first conductive semiconductor layer areselectively removed.
 16. The light emitting device of claim 8, whereinthe non-conductive semiconductor layer comprises an un-doped GaN layer.17. The light emitting device of claim 8, wherein the second lightextraction pattern is formed on the first conductive semiconductorlayer.
 18. The light emitting device of claim 9, wherein the firstelectrode layer is surrounded by the first conductive semiconductorlayer and the non-conductive semiconductor layer.
 19. A light emittingdevice, comprising: a light emitting semiconductor layer; a firstelectrode layer on the light emitting semiconductor layer; a secondelectrode layer under the light emitting semiconductor layer so that thelight emitting semiconductor layer is disposed between the first andsecond electrode layers; and a photonic crystal structure comprising afirst light extraction pattern having a first period on an average in atraveling direction of light emitted from the light emittingsemiconductor layer, and a second light extraction pattern having asecond period on an average, the first period being greater than λ/n,and the second period being identical to or smaller than λ/n, where n isa refractive index of a material comprising the photonic crystalstructure, and λ is a wavelength of the light emitted from the lightemitting semiconductor layer.
 20. The light emitting device of claim 19,wherein the first light extraction pattern and the second lightextraction pattern are formed in a hole shape or a protrusion shape,respectively.
 21. The light emitting device of claim 1, wherein n isabout 2.2 to about 2.3, and λ is about 450 nm to about 490 nm.
 22. Thelight emitting device of claim 8, wherein n is about 2.2 to about 2.3,and λ is about 450 nm to about 490 nm.
 23. The light emitting device ofclaim 19, wherein n is about 2.2 to about 2.3, and λ is about 450 nm toabout 490 nm.
 24. The light emitting device of claim 2, wherein thefirst electrode layer is formed in a hole of the first conductivesemiconductor layer.
 25. The light emitting device of claim 4, whereinthe protrusions are formed of silver.